Lactic acid bacteria that existed widely in the natural world are microbes of generating an organic acid by using a carbohydrate such as a glucose or lactose (von Wright, 2005). The Lactic acid bacterium has been directly or indirectly used in food from a long time ago. As a result of a research on an intestinal microflora of a man, it has been reported that the main Lactic acid bacteria in the gastrointestinal track of a healthy man are Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus fermentum, Lactobacillus plantarum and so on. Such Lactic acid bacteria are resistant to gastric acid and bile (Balcazar, 2007). Presently, the Lactic acid bacterium has been widely used as a microbial agent or vital cell preparation of fermented goods and so on all over the world. There are many reports about the cytotoxic effect of fermented milk or Lactic acid bacteria on tumour cells. For example, the administration of Lactobacillus casei can prevent the development of colorectal cancer, with a daily intake of live L. casei suppressing atypia of colorectal tumours in 398 men and women who were free from tumours and who had at least two colorectal tumours removed (Ishikawa et al., 2005). Lactic acid bacteria are the bacteria metabolizing carbohydrate and producing lactic acid thereby. These bacteria belong to facultative anaerobes or obligatory anaerobes which proliferate well under anaerobic conditions. A few commonly known genuses of Lactic acid bacteria are Streptococcus, Lactobacillus, Leuconostoc, Bifidobacteria and Pediococcus. A Streptococcus genus microorganism is a homofermentative bacterium that generates lactic acid by fermenting milk to suppress putrefying bacteria or pathogenic bacteria. A Lactobacillus genus microorganism is a bacilliform, and a homo- or heterofermentative bacterium, which is widely seen in the fermentation of dairy products or vegetables. A Leuconostoc genus microorganism, a diplococcus, is a heterofermentative bacterium and mostly involved in fermenting vegetables. A Bifidobacteria genus microorganism is an obligatory anaerobe which generates L(+) lactic acid useful for children's health, but it cannot survive under aerobic conditions (Holzapfel et al., 2001).
Many chemical compositions have been reported as an anti-tumour agent. However, these compositions not only destroy the tumour cells, but also destroy normal cells. Alternatively, surgical treatment is generally performed to remove tumour tissue. However, this could be difficult as this method does not remove the tumour tissues thoroughly. It is said that the actual condition of any therapy provides side effects and does not fully acquire the best results. For example, chemotherapy has been successfully used as neo-adjuvant, adjuvant and salvage strategies (Carlson et al., 2006). Chemotherapy targets rapidly dividing cancer cells, with deleterious side effect to rapidly dividing normal cells. This results in the most common side effects of chemotherapy such as endothelial toxicity, immunosuppression, mucositis and alopecia (Mitchell, 2004; Mailloux et al., 2005). Moreover, the use of conventional chemotherapeutic drugs has been proved to cause chemoresistance in cancer cells (Zhivotovsky and Orrenius, 2009). It is also used as concomitant treatment therapy with irradiation and biological agents (American Cancer Society, 2009). Despite much more advance in chemotherapy to surgery and irradiation, cancer mortality rate still ranks high among causes of mortality in many countries (WHO, 2009a). It is therefore essential to develop novel chemotherapeutics with greater efficacy while limited toxicity to normal cells.
The desire by consumers to use natural methods for health maintenance rather than long-term chemotherapeutics agents linked to their expectation that food becomes a source of prolonged well-being, supports the speculation that the probiotic market will expand rapidly. Results obtained from multidisciplinary research will probably essential for the positioning of probiotic preparations as either a food, a food supplement or as pharmaceutical preparation (Mercenier et al., 2002). Bacteriocins are isolated from Lactic acid bacteria and they exhibit inhibitory effects against various pathogens in a manner similar to antibiotics. However, bacteriocins are distinguishable from antibiotics in terms of their synthesis, mode of action, toxicity and resistance mechanisms.
New antitumour compound are continually in demand, for the treatment of cancer in man and the production of new anticancer compounds is an important feature of developing antitumour agents for further studies. Equally important are novel strains of cultures used in the production processes for preparing these compounds. Additionally, it has been determined that the metabolites produced by certain microorganism exhibited antimicrobial activity against important human pathogenic bacteria and fungi, as well as having antiviral and anti-tumour activities (Zhao et al., 2006; Wachsman et al., 1999).
An object of the present invention is to provide a novel antitumour agent which has excellent antitumour activity based on metabolites with reduced side effects and which can be prepared starting with a highly safe bacterium used in food production. Yet, another objective of this present invention provides methods of measuring anticancer efficacy (cancer-cell-growth inhibition and apoptosis induction) of Lactic acid bacteria, and further to provide screening method of the Lactic acid bacteria which have anticancer efficacy.